Endogenous Pacemakers and Exogenous Zeitgebers AO3

• RALPH supported the role of the SCN by breading MUTANT HAMSTERS with a 20hr s/w cycle + then transplanting into the brains of 'normal' hamsters, which changed their S/W to 20his too, so SCN v. important.
• ALSO, quite hard, to study endogenous pacemakers on their own e.g. SIFFRE used artificial light, so this could have impact.
• Perhaps the research (+ associated theories) had an lack validity.
• There is evidence AGAINST (Social cues as E.Z.-MILES Studied a man who had a 24.9 hr s/w cycle and social cues could NOT change this - not enough in isolacion.
• However, other research has strong suppore - CAMPBELL + MURPHY found light can be defected on skin (shone light on backs of knees) + could deviate ppls s/w cycle by up to 3 hours, so light is a powerful E.z.
• SCN/light is not as normal BIOLOGICALLY REDUCTIONIST - only factor in ARCTIC ORCLE, s/w cycle - perhaps people sleep when it's dark because it is more socially acceptable to conduct daily activities in daylight, so perhaps more consideration reeded.